Manipulating hydrophilicity of conventional dye molecules for water tracer applications

ABSTRACT

A composition includes a functionalized fluorescent dye. The functionalized fluorescent dye includes an isothiocyanate-containing dye that is functionalized with a functional group. The functional group includes a primary amine. The functionalized fluorescent dye can be mixed with a fluid to form a tracer fluid for tracing fluid flow in a subterranean formation.

TECHNICAL FIELD

This disclosure relates to methods and compositions used in generating and using functionalized fluorescent tracers in drilling and oil well applications.

BACKGROUND

Tracer techniques can be a powerful diagnostic tool in numerous scientific disciplines and for technologies in many industrial sectors. Molecular tracers can include water-soluble or oil-soluble compounds. In field tests of oilfields, water-soluble tracers can provide a better understanding of the studied oil reservoir, for example, a better understanding of inter-well connections, connections between layers and heterogeneities. Similarly, oil-soluble tracers can provide information on petroleum products, for example qualitative analysis of the production fluid return from multiple stage completions, either vertical or horizontal completions.

SUMMARY

This disclosure describes technologies relating to functionalized fluorescent tracers, methods of making the tracers, and methods of using the tracers. Certain aspects of the subject matter described can be implemented as a composition. The composition includes a functionalized fluorescent dye. The functionalized fluorescent dye includes an isothiocyanate-containing dye that is functionalized with a functional group. The functional group includes a primary amine. The isothiocyanate-containing dye is selected from the group consisting of fluorescein isothiocyanate, Rhodamine B isothiocyanate, or tetramethylrhodamine isothiocyanate, or any isoform thereof. The functional group is selected from Group I or Group II. Group I consists of aminomethanesulfonic acid, 2-aminoethanesulfonic acid, 3-amino-1-propanesulfonic acid, 2-aminoethyl(trimethyl)azanium, and 3-aminopropyl(trimethyl)azanium. Group II consists of 4-aminobenzenesulfonic acid, 3-aminobenzenesulfonic acid, 2-aminobenzenesulfonic acid, 3-amino-4-hydroxybenzenesulfonic acid, 4-amino-3-hydroxybenzenesulfonic acid, (4-aminophenyl)-trimethylazanium, 6-amino-4-hydroxy-2-naphthalenesulfonic acid, 1-amino-2-naphthol-4-sulfonic acid, 7-aminonaphthalene-1,3-disulfonic acid, 4-aminonaphthalene-1,7-disulfonic acid, 8-amino-1,3,6-naphthalenetrisulfonic acid, and 8-aminopyrene-1,3,6-trisulfonic acid.

This, and other aspects, can include one or more of the following features. In some implementations, the isothiocyanate-containing dye is Rhodamine B isothiocyanate, and the functional group is 4-aminobenzenesulfonic acid. In some implementations, the isothiocyanate-containing dye is fluorescein isothiocyanate, and the functional group is 2-aminoethyl(trimethyl)azanium. In some implementations, the isothiocyanate-containing dye is tetramethylrhodamine isothiocyanate, and the functional group is 2-aminoethanesulfonic acid.

Certain aspects of the subject matter described can be implemented as a method of making a functionalized fluorescent dye. A water-soluble isothiocyanate-containing fluorescent dye is dissolved in an aqueous solvent to yield an aqueous dye solution. The water-solutble isothiocyanate-containing fluorescent dye is selected from the group consisting of fluorescein isothiocyanate, Rhodamine B isothiocyanate, or tetramethylrhodamine isothiocyanate, or any isoform thereof. A functional group is dissolved in water to yield an aqueous functional group solution. The functional group includes a primary amine. The functional group is selected from Group I or Group II. Group I consists of aminomethanesulfonic acid, 2-aminoethanesulfonic acid, 3-amino-1-propanesulfonic acid, 2-aminoethyl(trimethyl)azanium, and 3-aminopropyl(trimethyl)azanium. Group II consists of 4-aminobenzenesulfonic acid, 3-aminobenzenesulfonic acid, 2-aminobenzenesulfonic acid, 3-amino-4-hydroxybenzenesulfonic acid, 4-amino-3-hydroxybenzenesulfonic acid, (4-aminophenyl)-trimethylazanium, 6-amino-4-hydroxy-2-naphthalenesulfonic acid, 1-amino-2-naphthol-4-sulfonic acid, 7-aminonaphthalene-1,3-disulfonic acid, 4-aminonaphthalene-1,7-disulfonic acid, 8-amino-1,3,6-naphthalenetrisulfonic acid, and 8-aminopyrene-1,3,6-trisulfonic acid. The aqueous dye solution and the aqueous functional group solution are mixed to form the functionalized fluorescent dye. The functionalized fluorescent dye is a reaction product of the water-soluble isothiocyanate-containing dye and the functional group.

This, and other aspects, can include one or more of the following features. The aqueous solvent can be a mixture of water and ethanol. In some implementations, a volumetric ratio of water to ethanol of the aqueous solvent is in a range of from 1:1 to 9:1. In some implementations, the water is deionized water.

Certain aspects of the subject matter described can be implemented as a method. A functionalized fluorescent tracer and a fluid are mixed to form a tracer fluid. The functionalized fluorescent tracer includes an isothiocyanate-containing dye that is functionalized with a functional group. The functional group includes a primary amine. The isothiocyanate-containing dye is selected from the group consisting of fluorescein isothiocyanate, Rhodamine B isothiocyanate, or tetramethylrhodamine isothiocyanate, or any isoform thereof. The functional group is selected from Group I or Group II. Group I consists of aminomethanesulfonic acid, 2-aminoethanesulfonic acid, 3-amino-1-propanesulfonic acid, 2-aminoethyl(trimethyl)azanium, and 3-aminopropyl(trimethyl)azanium. Group II consists of 4-aminobenzenesulfonic acid, 3-aminobenzenesulfonic acid, 2-aminobenzenesulfonic acid, 3-amino-4-hydroxybenzenesulfonic acid, 4-amino-3-hydroxybenzenesulfonic acid, (4-aminophenyl)-trimethylazanium, 6-amino-4-hydroxy-2-naphthalenesulfonic acid, 1-amino-2-naphthol-4-sulfonic acid, 7-aminonaphthalene-1,3-disulfonic acid, 4-aminonaphthalene-1,7-disulfonic acid, 8-amino-1,3,6-naphthalenetrisulfonic acid, and 8-aminopyrene-1,3,6-trisulfonic acid. The tracer fluid is flowed into a first subterranean formation. A sample is recovered from the first subterranean formation or a second subterranean formation that is connected to the first subterranean formation. The sample is analyzed for a fluorescent signal.

This, and other aspects, can include one or more of the following features. The functionalized fluorescent tracer can be identified in the sample using fluorescence (for example, fluorescence imaging or fluorescence spectroscopy), ultraviolet-visible (UV-Vis) spectroscopy, Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy, mass spectroscopy (MS), high performance liquid chromatography (HPLC), liquid chromatography-mass spectroscopy (LC-MS), or pyrolysis gas chromatography-mass spectroscopy (pyrolysis GC-MS), or any combination thereof. The sample can be a fluid sample, a solid sample, or a sample that includes both fluid and solid. The fluid (mixed with the functionalized fluorescent tracer) can be a fracking fluid or a drilling mud.

The details of one or more implementations of the subject matter of this disclosure are set forth in the accompanying drawings and the description. Other features, aspects, and advantages of the subject matter will become apparent from the description, the drawings, and the claims.

DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram of an example well.

FIG. 2 is a flow chart of an example method for making a functionalized fluorescent dye that can be used in the well of FIG. 1 .

FIG. 3 is a flow chart of an example method for treating a well.

FIG. 4 is a molecular structure of an example functionalized fluorescent dye.

FIG. 5 is a molecular structure of an example functionalized fluorescent dye.

FIG. 6 is a molecular structure of an example functionalized fluorescent dye.

DETAILED DESCRIPTION

This disclosure describes functionalized fluorescent tracers, methods of making the tracers, and methods of using the tracers. The functionalized fluorescent tracers can be used, for example, to track aqueous fluids in wells. A chemical method can be implemented to modify the structures of conventional fluorescent dye molecules by covalently bonding a hydrophilic functional group to the dye molecule, which can increase the fluorescent dye’s hydrophilicity. The resulting dye exhibits enhanced solubility in water while retaining its fluorescence. The hydrophilic functional group can also serve as a molecular identifier.

FIG. 1 depicts an example of a drilling operation 10 for a well 12. The well 12 can be in a wellbore 20 formed in a subterranean zone 14 of a geological formation in the Earth’s crust. The well 12 enables access to the subterranean zone 14 to allow recovery (that is, production) of fluids to the surface and, in some implementations, additionally or alternatively allows fluids to be placed in the Earth. The subterranean zone 14 can include, for example, a formation, a portion of a formation, or multiple formations in a hydrocarbon-bearing reservoir from which recovery operations can be practiced to recover trapped hydrocarbons. Examples of unconventional reservoirs include tight-gas sands, gas and oil shales, coalbed methane, heavy oil and tar sands, gas-hydrate deposits, to name a few. In some implementations, the subterranean zone 14 includes an underground formation including natural fractures 60 in rock formations containing hydrocarbons (for example, oil, gas, or both). For example, the subterranean zone 14 can include a fractured shale. In some implementations, the well 12 can intersect other suitable types of formations, including reservoirs that are not naturally fractured.

The well 12 can include a casing 22 and well head 24. The wellbore 20 can be a vertical, horizontal, deviated, or multilateral bore. The casing 22 can be cemented or otherwise suitably secured in the wellbore 20. Perforations 26 can be formed in the casing 22 at the level of the subterranean zone 14 to allow oil, gas, and by-products to flow into the well 12 and be produced to the surface 25. Perforations 26 can be formed using shape charges, a perforating gun, or otherwise.

For a drilling treatment 10, a work string 30 can be disposed in the wellbore 20. The work string 30 can be coiled tubing, sectioned pipe, or other suitable tubing. A drilling tool or drill bit 32 can be coupled to an end of the work string 30. Packers 36 can seal an annulus 38 of the wellbore 20 uphole of and downhole of the subterranean zone 14. Packers 36 can be mechanical, fluid inflatable, or other suitable packers.

One or more pump trucks 40 can be coupled to the work string 30 at the surface 25. The pump trucks 40 pump drilling mud 58 down the work string 30 to lubricate and cool the drilling tool or drill bit 32, maintain hydrostatic pressure in the wellbore, and carry subterranean cuttings to the surface. The drilling mud 58 can include a fluid pad, proppants, flush fluid, or a combination of these components. The pump trucks 40 can include mobile vehicles, equipment such as skids, or other suitable structures.

One or more instrument trucks 44 can also be provided at the surface 25. The instrument truck 44 can include a drilling control system 46 and a drilling simulator 47. The drilling control system 46 monitors and controls the drilling treatment 10. The drilling control system 46 can control the pump trucks 40 and fluid valves to stop and start the drilling treatment 10. The drilling control system 46 communicates with surface and subsurface instruments to monitor and control the drilling treatment 10. In some implementations, the surface and subsurface instruments may comprise surface sensors 48, down-hole sensors 50, and pump controls 52.

Additives 81 can be mixed with drilling mud 58 or other drilling fluids and flowed through the reservoir. In some implementations, the additives 81 can include one or more tracers, for example, a fluorescent dye. Fluorescent dyes can be used as water-soluble tracers. These dyes are inexpensive and easy to use. Examples of fluorescent dyes include fluorescein, eosin, Rhodamine, and Rhodamine-B. However, these organic dye-based tracers have some shortcomings, and in particular, in relation for use as water tracers. For example, the water-soluble tracers fluorescein, eosin, and Rhodamine can adsorb onto reservoir rock or partially dissolve in the oil phase. In addition, the number of tracers is limited to the number of organic dye molecules available.

The tracers described herein overcome these shortcomings. These tracers can be generated using a synthetic method to tune the hydrophilicity/hydrophobicity of water-soluble dye molecules by chemically modifying the molecular structure of the molecule. For example, by covalently grafting functional groups onto the dye molecules, the various functional groups can create barcoded structural information, resulting in new compounds. In some embodiments, by introducing hydrophilic functional groups into water-soluble dye molecules, the hydrophilicity of the resulting molecules can be enhanced, thus improving their solubility in an aqueous phase. By tailoring the molecules, the hydrophilicity and hydrophobicity of the molecule can be adjusted to a desired degree. Therefore, the partition of the molecule in an oil phase is controllable. This, in part, enables the potential application of these functionalized fluorescent dyes as partition tracers for oil reservoir applications. The structure-modified dyes reserve their fluorescence properties, although in some implementations the fluorescence features may also be modified by the introduction of functional groups. In some implementations, a hydrophilic functional group including a sulfonate anion or a quaternary ammonium cation can be introduced, resulting in dye compounds with low sorption on rock in fluids. Sulfonate anions and quaternary ammonium cations are highly hydrophilic and therefore highly soluble in water. Covalently bonding a functional group that includes one of these ions to the fluorescent dye can enhance the dye’s solubility in water.

These functionalized fluorescent dyes are described herein as barcoded or having barcode information. In this context, “barcode” refers to the fact that these functionalized dyes or tracers are uniquely identifiable two or more orthogonal analyses. As a first factor, the tracers can be identified by their fluorescence signal, for example, by the wavelength of the emission spectrum or simply by the presence of a fluorescent signal. As a second factor, the tracers can be identified by their mass or hydrophilicity. Accordingly, the unique combinations of the different fluorophores and the different functionalization groups results in a library of barcoded tracers.

Barcoded tracers have several advantages. For example, different combinations of different tracers can be used simultaneously or in parallel to provide information about drilling operations or subterranean formations. For example, two or more uniquely identifiable tracers can be injected at two or more different drilling sites and can yield information about inter well connectivity. In another example, uniquely identifiable tracers can be injected at the same drilling site at different times, can yield temporal information about transit time, depth, or length of subterranean fractures or formations.

Further, the two-factor nature of the barcode tracers allows for an advantageous two-factor analysis. The first factor, the fluorescence signal, can be detected in an initial, rapid analysis. Accordingly, samples recovered from a drilling operation or subterranean formation can be quickly and qualitative analyzed for the presence of a fluorescence signal, i.e., a ‘yes/no’ analysis. In some implementations, this first analysis can be done on-site, and samples exhibiting a fluorescence signal can be allocated for further processing. Next, the samples exhibiting a fluorescence signal can be subsequently separated and analyzed by mass or chromatographic methods, for example by high performance liquid chromatography (HPLC), mass spectrometry (MS), or liquid chromatography - mass spectrometry (LC-MS) analysis.

A chemical method to modify the structures of conventional dye molecules by introducing molecular barcode information and by tailoring the hydrophilicity and/or hydrophobicity of the conventional water-soluble dye molecules is described herein. The resulting compounds expand the number of dyes available for tracer applications as water-soluble tracers or partition tracers.

The new dye molecules include the general structure R_(I) - X - R_(II), where R_(I) is a fluorescent fluorophore. The fluorophore can be either hydrophilic or hydrophobic, and can be detectable by optical methods, for example, florescence imaging or molecular spectroscopy (absorbance or fluorescence). In the general structure, X can be a linking molecule. X can be selected from the group that includes C₁₋₁₈ alkylene, C₁₋₁₈ alkenylene, or C₁₋₁₈ alkynylene, where each of C₁₋₁₈ alkylene, C₁₋₁₈ alkenylene, or C₁₋₁₈ alkynylene can be optionally replaced or interrupted by any one of oxygen (O), sulfur (S), or an amine (NH). In some implementations, X is a thiourea. In the general structure, R_(II) can be selected from the group that includes hydrogen, alkoxy, haloalkoxy (including Cl, Br, or I), aryl, or heteroaryl (including N, NH, O, or S). The R_(II) confers a molecular fingerprint or barcode structure into the new compounds. The R_(I) - X - R_(II) compounds are detectable by spectroscopy and imaging methods, for example, UV-Visible spectroscopy (UV-Vis), fluorescence (such as fluorescence spectroscopy or fluorescence imaging), Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy, mass spectroscopy, or chromatography (such as HPLC, LC-MS, or pyrolysis GC-MS).

In some implementations, the fluorescent dye R_(I) is fluorescein isothiocyanate (FITC), Rhodamine B isothiocyanate (RBITC), tetramethylrhodamine isothiocyanate (MRITC or TRITC), 1,1′-bis(3-isothiocyanatopropyl)-11-chloro-4,5:4′,5′-dibenzo-3,3,3′,3′-tetramethyl-10,12-trimethylenindotricarbocyanine bromide (NIR 5e), eosin-5-isothiocyanate, or any isomer thereof. The structures of FITC, RBITC, and MRITC/TRITC are shown in Table 1. These dyes are highly water-soluble, i.e., hydrophilic, and have fluorescence emissions in the visible light spectral region. The excitation and emission wavelengths (in nanometers, nm) of these dyes are listed in Table 1.

TABLE 1 Water-Soluble Dyes and their Molecular Structure Dye compound Molecular structure; Molecular weight Fluorescence λexcitation/λemission CAS Number / Isomers Fluorescein isothiocyanate (FITC)

495 nm/519 nm 27072-45-3 (mixed isomers); 3326-32-7 (5-isomer); 18861-78-4 (6-isomer) Rhodamine B isothiocyanate (RBITC)

570 nm/595 nm 36877-69-7 (mixed isomers) Tetramethylrhodamine isothiocyanate (MRITC or TRITC)

544 nm/570 nm 95197-95-8 (mixed isomers); 80724-20-5 (Isomer R); 80724-19-2 (5-TRITC)

The dyes shown in Table 1 were each modified with additional functional groups. The functional groups are added using the reaction of a primary amine with an isothiocyanate to result in a substituted thiourea, as shown in Equation 1.

R_(II) is a hydrophilic functional group that includes a primary amine group and a sulfonate anion (or sulfonic acid) or a quaternary ammonium cation, or other suitable amine-containing hydrophilic functional group, and R_(I) is the isothiocyanate-containing fluorescent dye, where in Equation 1 the isothiocyanate group is expanded for clarity.

FIG. 2 is a flow chart of an example method 200 of making a functionalized fluorescent dye. The reactions were performed at room temperature in a bi-phase system. At block 202, a water-soluble isothiocyanate-containing fluorescent dye (such as FITC, RBITC, MRITC, or TRITC) is dissolved in an aqueous solvent to yield an aqueous dye solution. In some implementations, the aqueous dye solution at block 202 is deionized water. In some implementations, the aqueous dye solution at block 202 is a mixture of water and ethanol. For example, the aqueous dye solution at block 202 can be a water/ethanol mixture with a 9:1 volumetric ratio of water to ethanol. For example, the aqueous dye solution at block 202 can be a water/ethanol mixture with a 1:1 volumetric ratio of water to ethanol. At block 204, a functional group is dissolved in water to yield an aqueous functional group solution. For example, the functional group is dissolved in deionized water at block 204. The functional group at block 204 is hydrophilic and includes a primary amino group (amine compound). In some implementations, the amine compound at block 204 includes a hydrocarbon chain (examples are provided in Table 2) or an aromatic portion (examples are provided in Table 3). In some implementations, the amine compound at block 204 includes a sulfonate anion (or sulfonic acid) or a quaternary ammonium cation (examples are provided in both Table 2 and Table 3). The aqueous dye solution and the aqueous functional group solution each contain the same molecular molar concentration of fluorescent dye and the amine compound, respectively. At block 206, the aqueous dye solution and the aqueous functional group solution are mixed to form the functionalized fluorescent dye. In some implementations, the aqueous dye solution and the aqueous functional group solution are mixed in equal volumes at block 206 and stirred vigorously. In some implementations, the reaction between the fluorescent dye and the functional group is allowed to continue under stirring for at least 12 hours at block 206. The functionalized fluorescent dye formed at block 206 is a reaction product of the water-soluble isothiocyanate-containing dye and the amine-group containing hydrophilic functional group.

Tables 2 and 3 illustrate different amine-containing functional groups that can be used to functionalize an isothiocyanate dye. The compounds shown in Table 2 are nonaromatic compounds with primary amino groups and either a sulfonate anion (or sulfonic acid) or a quaternary ammonium cation. The compounds have different molecular weights and provide both barcode information and the ability to tailor the hydrophilicity and miscibility with water of the resulting compound, based on, for example, alkyl chain length. Accordingly, isothiocyanate dyes functionalized with the compounds listed in Table 2 can have variable partitioning in oil phases.

The compounds shown in Table 3 are aromatic compounds with primary amino groups and either a sulfonate anion (or sulfonic acid) or a quaternary ammonium cation. The compounds have different molecular weights and provide both barcode information and the ability to tailor the hydrophilicity and miscibility with water of the resulting compound, based on, for example, the number of cyclic rings and/or the number of sulfonate anions. Accordingly, isothiocyanate dyes functionalized with the compounds listed in Table 2 can have variable partitioning in oil phases.

TABLE 2 Nonaromatic Compounds with Primary Amino Groups Compound Molecular Structure/Weight (Daltons) CAS number Aminomethanesulfonic acid

13881-91-9 2-aminoethanesulfonic acid

107-35-7 3-amino-1-propanesulfonic acid

3687-18-1 2-aminoethyl(trimethyl)azanium

38170-37-5 3-aminopropyl(trimethyl)azanium

58999-88-5

TABLE 3 Aromatic Compounds with Primary Amino Groups Compound Molecular Structure/Weight (Daltons) CAS number 4-aminobenzenesulfonic acid

121-57-3 3-aminobenzenesulfonic acid

121-47-1 2-aminobenzenesulfonic acid

88-21-1 3-amino-4-hydroxybenzenesulfonic acid

98-37-3 4-amino-3-hydroxybenzenesulfonic acid

2592-14-5 (4-aminophenyl)-trimethylazanium

21248-43-1 6-amino-4-hydroxy-2-naphthalenesulfonic acid

90-51-7 4-amino-3-hydroxy-1-naphthalenesulfonic acid

116-63-2 7-aminonaphthalene-1,3-disulfonic acid

86-65-7 4-aminonaphthalene-1,7-disulfonic acid

85-74-5 8-amino-1,3,6-naphthalenetrisulfonic acid

117-42-0 8-aminopyrene-1,3,6-trisulfonic acid

51987-58-7

The dyes described herein can be used as water tracers in subterranean applications. For example, multistage hydraulic fracturing along a horizontal well is key to effectively recover hydrocarbons from tight reservoirs. Improving the hydrocarbon recovery requires detailed production information of each hydraulic fracture. Water-soluble chemical tracers are often used to calculate the production profile from multistage fracturing through a tracer flow back test. Further, these synthesized barcoded water-soluble compounds can also be added to mud formulations in water-based drilling fluids as mud tracers for mud logging applications.

With the barcoded water-soluble tracers described herein, qualitative analysis by fluorescence spectroscopy or imaging can be used for water tracing applications, for example, in single or inter-well test water flooding or in hydraulic fracturing, while detailed molecular barcode information can be revealed by HPLC, LC-MS, or pyrolysis GC-MS analysis to identify each tracer from different locations.

FIG. 3 is a flow chart of an example method 300 of tracing fluid flow in a subterranean formation. At block 302, a functionalized fluorescent tracer and a fluid are mixed to form a tracer fluid. At block 304, the tracer fluid is flowed into a first subterranean formation. At block 306, a sample is recovered from the first subterranean formation or a second subterranean formation connected to the first subterranean formation. At block 308, the sample is analyzed for a fluorescent signal. At block 310, the sample is analyzed for a barcode functional group. For example, the sample is analyzed at block 310 to identify the barcode functional group present in the functionalized fluorescent tracer.

Example 1

34.6 milligrams (mg) of 4-aminobenzenesulfonic acid was dissolved in 25 milliliters (mL) of deionized water, and 0.5 mL of ammonia water (NH₃·H₂O, 29.5 weight percent) was added to adjust the pH of the solution to about 9. 53.6 mg of RBITC was dissolved in 25 mL of a water/ethanol mixture with a 9:1 volumetric ratio of water to ethanol. The two solutions were mixed and reacted for more than 12 hours under vigorous stirring at room temperature. The molecular structure of the functionalized fluorescent dye is shown in FIG. 4 .

Example 2

35 mg of (2-aminoethyl)trimethylammonium chloride hydrochloride was dissolved in 25 mL of deionized water. 38.9 mg of FITC was dissolved in 25 mL of a water/ethanol mixture with a 1:1 volumetric ratio of water to ethanol. The two solutions were mixed and reacted for more than 12 hours under vigorous stirring at room temperature. The molecular structure of the functionalized fluorescent dye is shown in FIG. 5 .

Example 3

25 mg of 2-aminoethanesulfonic acid was dissolved in 25 mL of deionized water, and 0.5 mL of ammonia water (NH₃·H₂O, 29.5 weight percent) was added to adjust the pH of the solution to about 9. 44.4 mg of TRITC was dissolved in 25 mL of a water/ethanol mixture with a 9:1 volumetric ratio of water to ethanol. The two solutions were mixed and reacted for more than 12 hours under vigorous stirring at room temperature. The molecular structure of the functionalized fluorescent dye is shown in FIG. 6 .

Examples 1, 2, and 3 provide example procedures for making a functionalized fluorescent dye. With similar procedures, any one of the organic, fluorescent dyes shown in Table 1 can be combined with any one of the nonaromatic functional groups containing primary amino groups shown in Table 2 or any one of the aromatic functional groups containing primary amino groups shown in Table 3. The following includes example combinations of organic, fluorescent dyes and functional groups that can be combined to make a functionalized fluorescent dye. FITC and aminomethanesulfonic acid can be combined to make a functionalized fluorescent dye. FITC and 2-aminoethanesulfonic acid can be combined to make a functionalized fluorescent dye. FITC and 3-amino-1-propanesulfonic acid can be combined to make a functionalized fluorescent dye. FITC and 3-aminopropyl(trimethyl)azanium can be combined to make a functionalized fluorescent dye. FITC and 4-aminobenzenesulfonic acid can be combined to make a functionalized fluorescent dye. FITC and 3-aminobenzenesulfonic acid can be combined to make a functionalized fluorescent dye. FITC and 2-aminobenzenesulfonic acid can be combined to make a functionalized fluorescent dye. FITC and 3-amino-4-hydroxybenzenesulfonic acid can be combined to make a functionalized fluorescent dye. FITC and 4-amino-3-hydroxybenzenesulfonic acid can be combined to make a functionalized fluorescent dye. FITC and (4-aminophenyl)-trimethylazanium can be combined to make a functionalized fluorescent dye. FITC and 6-amino-4-hydroxy-2-naphthalenesulfonic acid can be combined to make a functionalized fluorescent dye. FITC and 4-amino-3-hydroxy-1-naphthalenesulfonic acid can be combined to make a functionalized fluorescent dye. FITC and 7-aminonaphthalene-1,3-disulfonic acid can be combined to make a functionalized fluorescent dye. FITC and 4-aminonaphthalene-1,7-disulfonic acid can be combined to make a functionalized fluorescent dye. FITC and 8-amino-1,3,6-naphthalenetrisulfonic acid can be combined to make a functionalized fluorescent dye. FITC and 8-aminopyrene-1,3,6-trisulfonic acid can be combined to make a functionalized fluorescent dye. RBITC and aminomethanesulfonic acid can be combined to make a functionalized fluorescent dye. RBITC and 2-aminoethanesulfonic acid can be combined to make a functionalized fluorescent dye. RBITC and 3-amino-1-propanesulfonic acid can be combined to make a functionalized fluorescent dye. RBITC and 2-aminoethyl(trimethyl)azanium can be combined to make a functionalized fluorescent dye. RBITC and 3-aminopropyl(trimethyl)azanium can be combined to make a functionalized fluorescent dye. RBITC and 3-aminobenzenesulfonic acid can be combined to make a functionalized fluorescent dye. RBITC and 2-aminobenzenesulfonic acid can be combined to make a functionalized fluorescent dye. RBITC and 3-amino-4-hydroxybenzenesulfonic acid can be combined to make a functionalized fluorescent dye. RBITC and 4-amino-3-hydroxybenzenesulfonic acid can be combined to make a functionalized fluorescent dye. RBITC and (4-aminophenyl)-trimethylazanium can be combined to make a functionalized fluorescent dye. RBITC and 6-amino-4-hydroxy-2-naphthalenesulfonic acid can be combined to make a functionalized fluorescent dye. RBITC and 4-amino-3-hydroxy-1-naphthalenesulfonic acid can be combined to make a functionalized fluorescent dye. RBITC and 7-aminonaphthalene-1,3-disulfonic acid can be combined to make a functionalized fluorescent dye. RBITC and 4-aminonaphthalene-1,7-disulfonic acid can be combined to make a functionalized fluorescent dye. RBITC and 8-amino-1,3,6-naphthalenetrisulfonic acid can be combined to make a functionalized fluorescent dye. RBITC and 8-aminopyrene-1,3,6-trisulfonic acid can be combined to make a functionalized fluorescent dye. TRITC and aminomethanesulfonic acid can be combined to make a functionalized fluorescent dye. TRITC and 3-amino-1-propanesulfonic acid can be combined to make a functionalized fluorescent dye. TRITC and 2-aminoethyl(trimethyl)azanium can be combined to make a functionalized fluorescent dye. TRITC and 3-aminopropyl(trimethyl)azanium can be combined to make a functionalized fluorescent dye. TRITC and 4-aminobenzenesulfonic acid can be combined to make a functionalized fluorescent dye. TRITC and 3-aminobenzenesulfonic acid can be combined to make a functionalized fluorescent dye. TRITC and 2-aminobenzenesulfonic acid can be combined to make a functionalized fluorescent dye. TRITC and 3-amino-4-hydroxybenzenesulfonic acid can be combined to make a functionalized fluorescent dye. TRITC and 4-amino-3-hydroxybenzenesulfonic acid can be combined to make a functionalized fluorescent dye. TRITC and (4-aminophenyl)-trimethylazanium can be combined to make a functionalized fluorescent dye. TRITC and 6-amino-4-hydroxy-2-naphthalenesulfonic acid can be combined to make a functionalized fluorescent dye. TRITC and 4-amino-3-hydroxy-1-naphthalenesulfonic acid can be combined to make a functionalized fluorescent dye. TRITC and 7-aminonaphthalene-1,3-disulfonic acid can be combined to make a functionalized fluorescent dye. TRITC and 4-aminonaphthalene-1,7-disulfonic acid can be combined to make a functionalized fluorescent dye. TRITC and 8-amino-1,3,6-naphthalenetrisulfonic acid can be combined to make a functionalized fluorescent dye. TRITC and 8-aminopyrene-1,3,6-trisulfonic acid can be combined to make a functionalized fluorescent dye.

While this specification contains many specific implementation details, these should not be construed as limitations on the scope of what may be claimed, but rather as descriptions of features that may be specific to particular implementations. Certain features that are described in this specification in the context of separate implementations can also be implemented, in combination, in a single implementation. Conversely, various features that are described in the context of a single implementation can also be implemented in multiple implementations, separately, or in any sub-combination. Moreover, although previously described features may be described as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can, in some cases, be excised from the combination, and the claimed combination may be directed to a sub-combination or variation of a sub-combination.

As used in this disclosure, the terms “a,” “an,” or “the” are used to include one or more than one unless the context clearly dictates otherwise. The term “or” is used to refer to a nonexclusive “or” unless otherwise indicated. The statement “at least one of A and B” has the same meaning as “A, B, or A and B.” In addition, it is to be understood that the phraseology or terminology employed in this disclosure, and not otherwise defined, is for the purpose of description only and not of limitation. Any use of section headings is intended to aid reading of the document and is not to be interpreted as limiting; information that is relevant to a section heading may occur within or outside of that particular section.

As used in this disclosure, the term “about” or “approximately” can allow for a degree of variability in a value or range, for example, within 10%, within 5%, or within 1% of a stated value or of a stated limit of a range.

As used in this disclosure, the term “substantially” refers to a majority of, or mostly, as in at least about 50%, 60%, 70%, 80%, 90%, 95%, 96%, 97%, 98%, 99%, 99.5%, 99.9%, 99.99%, or at least about 99.999% or more.

Values expressed in a range format should be interpreted in a flexible manner to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited. For example, a range of “0.1% to about 5%” or “0.1% to 5%” should be interpreted to include about 0.1% to about 5%, as well as the individual values (for example, 1%, 2%, 3%, and 4%) and the sub-ranges (for example, 0.1% to 0.5%, 1.1% to 2.2%, 3.3% to 4.4%) within the indicated range. The statement “X to Y” has the same meaning as “about X to about Y,” unless indicated otherwise. Likewise, the statement “X, Y, or Z” has the same meaning as “about X, about Y, or about Z,” unless indicated otherwise.

The term “downhole” as used in this disclosure refers to under the surface of the earth, such as a location within or fluidly connected to a wellbore.

As used in this disclosure, the term “drilling fluid” refers to fluids, slurries, or muds used in drilling operations downhole, such as during the formation of the wellbore.

As used in this disclosure, the term “fluid” refers to gases, liquids, gels, and any combination of these, unless otherwise indicated.

As used in this disclosure, the term “subterranean material” or “subterranean zone” or “subterranean formation” refers to any material under the surface of the earth, including under the surface of the bottom of the ocean. For example, a subterranean zone or material can be any section of a wellbore and any section of a subterranean petroleum- or water-producing formation or region in fluid contact with the wellbore. Placing a material in a subterranean zone can include contacting the material with any section of a wellbore or with any subterranean region in fluid contact the material. Subterranean materials can include any materials placed into the wellbore such as cement, drill shafts, liners, tubing, casing, or screens; placing a material in a subterranean zone can include contacting with such subterranean materials. In some examples, a subterranean zone or material can be any downhole region that can produce liquid and/or gaseous petroleum materials, water, or any downhole section in fluid contact with liquid or gaseous petroleum materials, or water. For example, a subterranean zone or material can be at least one of an area desired to be fractured, a fracture or an area surrounding a fracture, and a flow pathway or an area surrounding a flow pathway, in which a fracture or a flow pathway can be optionally fluidly connected to a subterranean petroleum- or water-producing region, directly or through one or more fractures or flow pathways.

As used in this disclosure, “treatment of a subterranean zone” can include any activity directed to extraction of water or petroleum materials from a subterranean petroleum- or water-producing formation or region, for example, including drilling, stimulation, hydraulic fracturing, clean-up, acidizing, completion, cementing, remedial treatment, abandonment, aquifer remediation, identifying oil rich regions via imaging techniques, and the like.

As used in this disclosure, a “flow pathway” downhole can include any suitable subterranean flow pathway through which two subterranean locations are in fluid connection. The flow pathway can be sufficient for petroleum and/or water to flow from one subterranean location to the wellbore or vice-versa. A flow pathway can include at least one of a hydraulic fracture, and a fluid connection across a screen, across gravel pack, across proppant, including across resin-bonded proppant or proppant deposited in a fracture, and across sand. A flow pathway can include a natural subterranean passageway through which fluids can flow. In some implementations, a flow pathway can be a water source and can include water. In some implementations, a flow pathway can be a petroleum source and can include petroleum. In some implementations, a flow pathway can be sufficient to divert water, a downhole fluid, or a produced hydrocarbon from a wellbore, fracture, or flow pathway connected to the pathway.

As used in this disclosure, “weight percent” (wt. %) can be considered a mass fraction or a mass ratio of a substance to the total mixture or composition. Weight percent can be a weight-to-weight ratio or mass-to-mass ratio, unless indicated otherwise.

Particular implementations of the subject matter have been described. Other implementations, alterations, and permutations of the described implementations are within the scope of the following claims as will be apparent to those skilled in the art. While operations are depicted in the drawings or claims in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed (some operations may be considered optional), to achieve desirable results. In certain circumstances, multitasking or parallel processing (or a combination of multitasking and parallel processing) may be advantageous and performed as deemed appropriate.

Moreover, the separation or integration of various system modules and components in the previously described implementations should not be understood as requiring such separation or integration in all implementations, and it should be understood that the described components and systems can generally be integrated together or packaged into multiple products.

Accordingly, the previously described example implementations do not define or constrain the present disclosure. Other changes, substitutions, and alterations are also possible without departing from the spirit and scope of the present disclosure. 

What is claimed is:
 1. A composition comprising: a functionalized fluorescent dye, wherein the functionalized fluorescent dye comprises an isothiocyanate-containing dye functionalized with a functional group comprising a primary amine, wherein: the isothiocyanate-containing dye is selected from the group consisting of fluorescein isothiocyanate, Rhodamine B isothiocyanate, or tetramethylrhodamine isothiocyanate, or any isoform thereof; and the functional group is selected from Group I or Group II, wherein: Group I consists of aminomethanesulfonic acid, 2-aminoethanesulfonic acid, 3-amino-1-propanesulfonic acid, 2-aminoethyl(trimethyl)azanium, and 3-aminopropyl(trimethyl)azanium; and Group II consists of 4-aminobenzenesulfonic acid, 3-aminobenzenesulfonic acid, 2-aminobenzenesulfonic acid, 3-amino-4-hydroxybenzenesulfonic acid, 4-amino-3-hydroxybenzenesulfonic acid, (4-aminophenyl)-trimethylazanium, 6-amino-4-hydroxy-2-naphthalenesulfonic acid, 1-amino-2-naphthol-4-sulfonic acid, 7-aminonaphthalene-1,3-disulfonic acid, 4-aminonaphthalene-1,7-disulfonic acid, 8-amino-1,3,6-naphthalenetrisulfonic acid, and 8-aminopyrene-1,3,6-trisulfonic acid.
 2. The composition of claim 1, wherein the isothiocyanate-containing dye is Rhodamine B isothiocyanate, and the functional group is 4-aminobenzenesulfonic acid.
 3. The composition of claim 1, wherein the isothiocyanate-containing dye is fluorescein isothiocyanate, and the functional group is 2-aminoethyl(trimethyl)azanium.
 4. The composition of claim 1, wherein the isothiocyanate-containing dye is tetramethylrhodamine isothiocyanate, and the functional group is 2-aminoethanesulfonic acid.
 5. A method of making a functionalized fluorescent dye, comprising: dissolving a water-soluble isothiocyanate-containing fluorescent dye in an aqueous solvent to yield an aqueous dye solution, wherein the water-soluble isothiocyanate-containing fluorescent dye is selected from the group consisting of fluorescein isothiocyanate, Rhodamine B isothiocyanate, or tetramethylrhodamine isothiocyanate, or any isoform thereof; dissolving a functional group in water to yield an aqueous functional group solution, wherein the functional group comprises a primary amine and is selected from Group I or Group II, wherein: Group I consists of aminomethanesulfonic acid, 2-aminoethanesulfonic acid, 3-amino-1-propanesulfonic acid, 2-aminoethyl(trimethyl)azanium, and 3-aminopropyl(trimethyl)azanium; and Group II consists of 4-aminobenzenesulfonic acid, 3-aminobenzenesulfonic acid, 2-aminobenzenesulfonic acid, 3-amino-4-hydroxybenzenesulfonic acid, 4-amino-3-hydroxybenzenesulfonic acid, (4-aminophenyl)-trimethylazanium, 6-amino-4-hydroxy-2-naphthalenesulfonic acid, 4-amino-3-hydroxy-1-naphthalenesulfonic acid, 7-aminonaphthalene-1,3-disulfonic acid, 4-aminonaphthalene-1,7-disulfonic acid, 8-amino-1,3,6-naphthalenetrisulfonic acid, and 8-aminopyrene-1,3,6-trisulfonic acid; and mixing the aqueous dye solution and the aqueous functional group solution to form the functionalized fluorescent dye, wherein the functionalized fluorescent dye is a reaction product of the water-soluble isothiocyanate-containing dye and the functional group.
 6. The method of claim 5, wherein the aqueous solvent is a mixture of water and ethanol.
 7. The method of claim 6, wherein a volumetric ratio of water to ethanol of the aqueous solvent is in a range of from 1:1 to 9:1.
 8. The method of claim 5, wherein the water is deionized water.
 9. A method of tracing fluid flow in a subterranean formation, comprising: mixing a functionalized fluorescent tracer and a fluid to yield a tracer fluid, wherein the functionalized fluorescent tracer comprises an isothiocyanate-containing dye functionalized with a functional group comprising a primary amine, wherein: the isothiocyanate-containing dye is selected from the group consisting of fluorescein isothiocyanate, Rhodamine B isothiocyanate, or tetramethylrhodamine isothiocyanate, or any isoform thereof; and the functional group is selected from Group I or Group II, wherein: Group I consists of aminomethanesulfonic acid, 2-aminoethanesulfonic acid, 3-amino-1-propanesulfonic acid, 2-aminoethyl(trimethyl)azanium, and 3-aminopropyl(trimethyl)azanium; and Group II consists of 4-aminobenzenesulfonic acid, 3-aminobenzenesulfonic acid, 2-aminobenzenesulfonic acid, 3-amino-4-hydroxybenzenesulfonic acid, 4-amino-3-hydroxybenzenesulfonic acid, (4-aminophenyl)-trimethylazanium, 6-amino-4-hydroxy-2-naphthalenesulfonic acid, 4-amino-3-hydroxy-1-naphthalenesulfonic acid, 7-aminonaphthalene-1,3-disulfonic acid, 4-aminonaphthalene-1,7-disulfonic acid, 8-amino-1,3,6-naphthalenetrisulfonic acid, and 8-aminopyrene-1,3,6-trisulfonic acid; flowing the tracer fluid into a first subterranean formation; recovering a sample from the first subterranean formation or a second subterranean formation connected to the first subterranean formation; and analyzing the sample for a fluorescent signal.
 10. The method of claim 9, comprising identifying the functionalized fluorescent tracer in the sample using fluorescence imaging, fluorescence spectroscopy, ultraviolet-visible (UV-Vis) spectroscopy, Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy, mass spectroscopy (MS), high performance liquid chromatography (HPLC), liquid chromatography-mass spectroscopy (LC-MS), or pyrolysis gas chromatography-mass spectroscopy (pyrolysis GC-MS), or any combination thereof.
 11. The method of claim 9, where in the sample is a fluid sample.
 12. The method of claim 9, wherein the fluid is a fracking fluid.
 13. The method of claim 9, wherein the fluid is a drilling mud. 